[S390] cio: fix ccw group device cleanup

Fix ccw group device initialization: initialize device object before
using reference counting during cleanup.

Fixes the following message when group device initialization fails
(e.g. because too few devices where specified):

  kobject: '<NULL>' (..): is not initialized, yet kobject_put() is
           being called.

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>